Working vehicle

ABSTRACT

In a working vehicle, a variable output HST and a planetary gear unit are connected with an engine, which is supported on a vehicle frame closer to a first side of a fore and aft direction of the vehicle in vibration free manner so as to together constitute a driving-side unit, which is integrally supported on the vehicle frame in vibration free manner. A transmission case of a transmission is fixedly supported on the vehicle frame closer to a second side of the fore and aft direction of the vehicle with a distance from the driving-side unit. An output element of the planetary gear unit is operatively connected with a wheel drive train of the transmission via a shaft coupling extending along the fore and aft direction of the vehicle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a working vehicle with a transmissionarrangement that transmits drive power from an engine to a drive axle.

2. Related Art

A vehicle such as a working vehicle is designed so as to transmit drivepower from an engine to a drive axle via a speed change unit, enablingthe drive axle to be rotated at a desired speed by operating the speedchange unit. Where it is desired to widen a speed change range of thedrive axle, and/or reduce the load applied to the speed change unit, asub-speed change unit is provided in addition to a main-speed changeunit.

FIG. 19 illustrates a model view of a conventional vehicle with themain- and sub-speed change units provided and a rear axle serving as thedrive axle. As illustrated in FIG. 19, aligned in the conventionalvehicle equipped with the sub-speed change unit from a first side to asecond side relative to a fore and aft direction of the vehicle areengine 801, flywheel 802, main-speed change unit 803, sub-speed changeunit 804 and driving axle unit 805, which are connected in tandem insuch a manner as to be separable from each other. This specificarrangement may cause a problem as mentioned below.

In the conventional vehicle with the sub-speed change unit, theindependent units, that is, the engine 801, the flywheel 802, themain-speed change unit 803, the sub-speed change unit 804 and the axleunit 805 respectively have housings, through which they are connected intandem, resulting in generating substantially no space between front andrear wheels. This causes a need to mount a step bar or board for thedriver's seat above either of the housings, which arrangement causes thestep bar or board to be mounted at a higher position, and or all of thehousings to be mounted at a higher place in case where a mid-mount moweris provided between the front and rear wheels, thus undesirably invitinga higher center of gravity.

Also, in the conventional arrangement, where an HST (Hydro-statictransmission) is used as the main-speed change unit 803, the HST itselfvibrates due to pulsation or the like of working fluid circulatedtherein. This vibration of the HST may be transmitted to vehicle frame800 via the sub-speed change unit 804 and the axle unit 805 because themain-speed change unit 803, the sub-speed change unit 804 and the axleunit 805 are connected in tandem, as described above. As a result, theride quality of the vehicle may be deteriorated.

To address the above problems, there has been proposed an arrangementwhere the engine is connected with the sub-speed change unit through ahousing, and the HST serving as the main-speed change unit is connectedwith a front side of the sub-speed change unit via a vibration absorbingmember, while a front side of the HST is connected with the housing viaanother vibration absorbing member. However, in this arrangement,vibration of the engine is not taken into account at all. Accordingly,there cause a problem that the housing itself, which supports the HSTthrough the vibration absorbing arrangement, vibrates due to vibrationtransmitted from the engine.

According to need and/or desire, the working vehicle is equipped with ahydraulic lift unit for lifting a working implement. Hitherto, thehydraulic lift unit is mounted on an upper side of a transmission caseof a transmission or inside of the transmission case. In thisarrangement, load generated when the working implement is moved upwardor downward is applied on the transmission case. For this reason, thetransmission case must be strengthened in this conventional arrangement.

In order to address the above problems, it is an object of the presentinvention to provide a working vehicle with a transmission arrangementtransmitting drive power from the engine to the drive axle via the main-and sub-speed change units, which is capable of widening the speedchange range of the drive axle and/or reducing load of a speed changemechanism, as well as effectively limiting expansion of the vehicle'slength while securing a free space between the front and rear wheels.

It is another object of the present invention to provide a workingvehicle that is capable of effectively preventing transmission ofvibration from the engine, the main-speed change unit or the like to thetransmission, the axle or the like, thus avoiding discomfort to thedriver of the vehicle.

It is still another object of the present invention to provide a workingvehicle equipped with a hydraulic lift unit for moving a workingimplement relative to the vehicle frame, which is capable of reducingthe load to the transmission case, which is generated by the movement ofthe working implement.

It is yet another object of the present invention to provide a workingvehicle equipped with an HMT made up by the combination of a variableoutput HST and a planetary gear unit, which is capable of minimizing thesize of the HST, and widening the running speed changing range, whileeasily producing freewheel state of the driving wheels.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided aworking vehicle, which includes a vehicle frame; an engine supported invibration free manner on the vehicle frame closer to a first side of afore and aft direction of the vehicle; a variable output HST having aninput shaft and an output shaft, the input shaft being operativelyconnected with the engine; a planetary gear unit including first tothird elements comprising a sun gear, a planetary carrier and aninternal gear, in which the first element and the second element of thethree elements are respectively operatively connected with the inputshaft and the output shaft of the HST; and a transmission including atransmission case and a drive train for driving wheels, the drive trainbeing placed within the transmission case and including aforward/rearward travel direction changing unit. In this arrangement,the HST and the planetary gear unit are connected with the engine so asto together constitute a driving-side unit; the transmission case isfixedly supported on the vehicle frame closer to a second side of thefore and aft direction of the vehicle with a distance from thedriving-side unit; and the third element of the planetary gear unit isoperatively connected with the drive train of the transmission via acoupling shaft for a running-power transmission path, which extendsalong the fore and aft direction of the vehicle.

Preferably, the transmission further includes a power take-off drivetrain being placed within the transmission case for taking off of drivepower for a working implement, and the input shaft of the HST isoperatively connected with the power take-off drive train via a shaftcoupling for a working-implement drive train, which extends along thefore and aft direction of the vehicle. More preferably, the shaftcoupling for the running-power transmission path is a vibrationabsorbing shaft coupling.

According to another aspect of the present invention, there is provideda working vehicle equipped with a hydraulic lift unit for moving aworking implement, which is to be attached to the working vehicle,relative to a vehicle frame, in which the vehicle frame includes a pairof main frames that extend in the fore and aft direction of the vehicleon the opposite lateral sides thereof and a cross member located closerto a first side of a fore and aft direction of the vehicle in such amanner as to straddle the pair of main frames; and the hydraulic liftunit is supported by the cross member.

Preferably, the vehicle frame further includes a ROPS support frame, theROPS support frame including a pair of vertical extensions respectivelyconnected with the pair of main frames, and an upper plate forconnection between upper ends of the pair of vertical extensions. Morepreferably, the ROPS support frame further includes a bottom plate forconnection between lower ends of the pair of vertical extensions; and atow-bar storage box, into which a tow bar is inserted, is secured to thebottom plate.

Preferably, the vehicle frame further includes a reinforcing framehaving a gate-like shape and being connected between the pair of mainframes; and the reinforcing frame has opposite lateral side wallportions, to which loader masts are attachable, and top wall portions,to which a handle column is attachable.

According to still another aspect of the present invention, there isprovided a working vehicle comprising an HMT made up by the combinationof an HST and a planetary gear unit, and a forward/rearward traveldirection changing unit for changing the rotational direction of outputof the HMT, the HMT and the forward/rearward travel direction changingunit being arranged in tandem in a power transmission path extendingfrom a driving source to driving wheels. The HST includes a hydraulicpump unit and a hydraulic motor unit, at least one of which beingdesignated as being of a variable displacement type, a pump shaft beingoperatively connected with the driving source for driving the hydraulicpump unit and a motor shaft being driven by the hydraulic motor unit,wherein an HST variable output in both forward and reverse directions isoutputted via the motor shaft. The HMT is designed to be held in asubstantially output shutdown mode during the HST variable output is ata maximum level in either forward or reverse direction, and switchedfrom the substantially output shutdown mode to a maximum output mode asthe HST variable output is changed from the maximum output level in theeither forward or reverse direction to a maximum output level in theopposite direction. The forward/rearward travel direction changing unitis designed to shut off the power transmission path during the HMT isheld in the substantially output shutdown mode, thereby enabling thedriving wheels to be brought into freewheel state.

In one embodiment of the working vehicle having the above arrangement,the forward/rearward travel direction changing unit is designed to bringthe driving wheels into freewheel state automatically, when the HMT hasbeen brought into the output shutdown mode. In another embodiment, theforward/rearward travel direction changing unit is designed to bring thedriving wheels into freewheel state by the operation from the outside,when the HMT has been brought into the output shutdown mode.

Preferably, the HMT is located closer to a first side of a fore and aftdirection of the vehicle frame and connected with the driving sourcethat is supported in vibration free manner relative to the vehicleframe, thereby constituting a driving-side unit in cooperation with thedriving source; and the forward/rearward travel direction changing unitis placed within a transmission case, the transmission case beingfixedly supported on the vehicle frame closer to a second side of thefore and aft direction of the vehicle frame with a distance from thedriving-side unit.

According to yet another aspect of the present invention, there isprovided a working vehicle comprising an HMT made up by the combinationof an HST and a planetary gear unit, and a forward/rearward traveldirection changing unit for changing the rotational direction of outputof the HMT, the HMT and the forward/rearward travel direction changingunit being arranged in tandem in a power transmission path extendingfrom a driving source to driving wheels. The HST includes a hydraulicpump unit and a hydraulic motor unit, at least one of which beingdesignated as being of a variable displacement type, a pump shaft beingoperatively connected with the driving source for driving the hydraulicpump unit and a motor shaft being driven by the hydraulic motor unit,wherein an HST variable output in both forward and reverse directions isoutputted via the motor shaft. The HMT is designed to be held in asubstantially output shutdown mode during the HST variable output is ata maximum level in either forward or reverse direction, and switchedfrom the substantially output shutdown mode to a maximum output mode asthe HST variable output is changed from the maximum output level in theeither forward or reverse direction to a maximum output level in theopposite direction. The forward/rearward travel direction changing unitis interposed between the driving source and the HMT with respect to apower transmission direction, and designed to be switched into a forwardtravel mode enabling transmission of drive power from the driving sourceto the pump shaft with the rotational direction of the drive powermaintained in a forward direction, a rearward travel mode enabling drivepower from the driving source to the pump shaft with the rotationaldirection of the drive power changed to a reverse direction, and aneutral mode shutting off a power transmission path from the drivingsource to the pump shaft.

Preferably, the driving source, the forward/rearward travel directionchanging unit and the HMT together constitute a driving-side unit thatis supported in vibration free manner relative to a vehicle frame.

In one embodiment of the above working vehicle, the forward/rearwardtravel direction changing unit is designed to be capable of selecting anormal operation, in which the forward/rearward travel directionchanging unit is switched into respectively the forward travel mode, therearward travel mode and the neutral mode when an operation member isshifted into a forward travel position, a rearward travel position and aneutral position by a driver, and a power neutral operation, in whichthe forward/rearward travel direction changing unit is switched intorespectively the forward travel mode and the rearward travel mode whenthe operation member is shifted into the forward travel position and therearward travel position by the driver, and switched into either theforward travel mode or the rearward travel mode when the operationmember is shifted to the neutral position.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, and other objects, features and advantages of the presentinvention will become apparent from the detailed description thereof inconjunction with the accompanying drawings wherein.

FIG. 1 is a schematic side view of a working vehicle according to oneembodiment of the present invention.

FIG. 2 is a model view of a power transmission path of the workingvehicle as illustrated in FIG. 1.

FIG. 3 is an exploded perspective view of an engine and an HMT in theworking vehicle of FIG. 1.

FIG. 4 is a longitudinal cross-sectional side view of the HMT in theworking vehicle of FIG. 1.

FIG. 5 is a graph showing the relationship between slant angle of anoutput adjustment member in the HST and rotational speed of an outputshaft of the HMT.

FIG. 6 is an exploded perspective view of a part of the vehicle frame inthe working vehicle of FIG. 1.

FIG. 7 is a hydraulic circuit diagram of an auxiliary pump unit in theworking vehicle of FIG. 1.

FIG. 8 is a plan view of a hydraulic lift unit and its proximity in theworking vehicle of FIG. 1.

FIG. 9 is a side view of the hydraulic lift unit and its proximity inthe working vehicle of FIG. 1.

FIG. 10 is a speed-change control circuit diagram of the working vehicleof FIG. 1.

FIG. 11 is the speed-change control circuit diagram employing a controlmethod different from that of FIG. 10.

FIG. 12 is a part of a hydraulic circuit diagram of a forward/rearwardtravel switching unit according to another embodiment of the presentinvention.

FIG. 13 is a schematic side view of the working vehicle according tostill another embodiment of the present invention.

FIG. 14 is a model view of a power transmission path of the workingvehicle as illustrated in FIG. 13.

FIG. 15 is a longitudinal cross-sectional side view of the HMT and itsproximity in the working vehicle of FIG. 13.

FIG. 16 is a cross section taken along line XVI-XVI in FIG. 15.

FIG. 17 is a speed change control circuit diagram in the working vehicleof FIG. 13.

FIG. 18 is another speed change control circuit diagram of the workingvehicle as illustrated in FIG. 13.

FIG. 19 is a schematic side view of the conventional working vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment

The description will be made for the first embodiment of the presentinvention with reference to the accompanied drawings. FIGS. 1 and 2 arerespectively a schematic side view of working vehicle 1 according tothis embodiment and a model view of its power transmission path.

As illustrated in FIGS. 1 and 2, the working vehicle 1 includes vehicleframe 10, engine 20 supported on the vehicle frame 10 closer to a firstside of the fore and aft direction of the vehicle in vibration freemanner, main-speed change unit 30 for changing the speed of drive powerfrom the engine and transmitting the same to a downstream unit, andtransmission 40 for driving the drive axle upon receiving output of themain-speed change unit. As illustrated in FIG. 2, the working vehicle 1includes an HMT (Hydro-mechanical transmission) unit made up by theconnection of HST 300 with planetary gear unit 350.

FIG. 3 is an exploded perspective view of the engine as viewed from therear side. As illustrated in FIGS. 1 and 3, the vehicle frame 10includes a pair of main frames 11 extending in the fore and aftdirection of the vehicle on the opposite lateral side thereof, while theengine 20 is supported on the pair of main frames 11 in vibration freemanner.

Specifically, the engine 20 is of the horizontal type with an engineoutput shaft extending along the fore and aft direction of the vehicle.The engine 20 has a crank case and is provided with bracket 20 a securedto a forward lower portion of a side wall of the crank case via rubbercushion 111 so that the engine is supported through the bracket 20 a andthe rubber cushion 111 on the pair of main frames 11, thus preventingtransmission of vibration from the engine 20 to the vehicle frame 10.

FIG. 4 is a longitudinal cross-sectional side view of the HST 300, theplanetary gear unit 350, and their proximity. The HST 300 includes inputshaft (pump shaft) 301 for receiving drive power from the engine 20 viaflywheel 60, hydraulic pump unit 310 being driven by the input shaft301, hydraulic motor unit 320 for non-stepwisely changing the speed ofdrive power from the engine 20 in cooperation with the hydraulic pumpunit 310, output shaft (motor shaft) 302 being rotated by the hydraulicmotor unit 320, center section 330 for supporting the hydraulic pumpunit 310 and the hydraulic motor unit 320, as well as forming therein ahydraulic circuit enabling fluid connection therebetween, and HST case340 being connected with the center section 330 so as to enclose thehydraulic pump unit 310 and the hydraulic motor unit 320. In thisembodiment, the center section 330 forms therein a pair of hydrauliclines serving as the hydraulic circuit, as will be describedhereinafter.

At least one of the hydraulic pump unit 310 and the hydraulic motor unit320 is of a variable displacement type that enables variation in theinflow/outflow amounts of hydraulic fluid through the operation of anoutput adjustment member. Specifically, the slant angle of the outputadjustment member is controlled so that drive power with its speednon-stepwisely changed according to the slant angle can be outputtedfrom the motor shaft 302, which is driven by the hydraulic motor unit320. In this embodiment, the hydraulic pump unit 310 and the hydraulicmotor unit 320 are respectively designated as being of the variabledisplacement type and a fixed displacement type.

The center section 330 has first side 331 and second side 332respectively facing the upstream and downstream sides of the powertransmission direction, in which the first side 331 supports thereonboth the hydraulic pump unit 310 and the hydraulic motor unit 320. TheHST case 340 is connected with the first side 331, thereby enclosing thehydraulic pump unit 310 and the hydraulic motor unit 320.

As used throughout the description, the directional term “upstream” and“downstream” are relative to the power transmission direction.

The input shaft 301 is rotatably supported by the center section 330 andthe HST case 340 so as to have an upstream end extending upstream fromthe HST case 340, and a downstream end extending downstream through thecenter section 330. Thus, the input shaft 301 has a rotational axisextending in the fore and aft direction of the vehicle.

The upstream end of the input shaft 301 is operatively connected withthe engine 20 via the flywheel 60. The flywheel 60 may be provided withdamper 61, which enables power transmission to the subsequent units,that is, the HST 300 and the planetary gear unit 350 which constitutesan HMT in cooperation with the HST 300, while limiting the variation inangular speed of the engine output shaft.

The hydraulic pump unit 310 includes piston unit 311 that is rotatedaround the axis of the input shaft 301 by the rotation of the inputshaft 301 and reciprocatingly moved in association with this rotationalmovement, cylinder block 312 that reciprocatingly supports the pistonunit 311, while being rotatably and slidably supported on the first side331 of the center section 330 so as to be communicated with the pair ofhydraulic lines, and output adjustment member 313 that limits the strokelength of the piston unit 311 through its slant angle, thereby varyingthe suction/discharge rate of the piston unit 311. The slant angle ofthe output adjustment member 313 is controlled by a hereinaftermentioned hydraulic control unit.

In this embodiment, the hydraulic pump unit 310 is designated as beingof an axial piston type, and therefore a movable swash plate is employedas the output adjustment member 313. Therefore, where a hydraulic pumpunit of a radial piston type is employed, a cam ring is employed as theoutput adjustment member.

The hydraulic motor unit 320, which is designated as being of the fixeddisplacement type in this embodiment, includes cylinder block 322 thatis rotatably and slidably supported on the first side 331 of the centersection 330 so as to be communicated with the pair of hydraulic lines,and piston unit 321 that is slidably supported within the cylinder block322, while being reciprocated and simultaneously rotated upon receivingpressurized hydraulic fluid from the pair of hydraulic lines, therebytransmitting this rotational movement to the output shaft.

The output shaft 302 is supported by the HST case 340 and the centersection 330 so as to have a downstream end extending through the centersection 330 to the outside (rearwards in this embodiment), and has therotational axis in the fore and aft direction of the vehicle so as to bein parallel relationship with the input shaft 301.

The working vehicle 1 is also provided on the front side of the HST case340 with charge pump unit 70 that is driven through the upstream end ofthe input shaft 301, as illustrated in FIGS. 2 and 4. The charge pumpunit 70 is used for supplying working fluid to the HST 30 and thehydraulic control unit that controls the output adjustment member.

The planetary gear unit 350 includes sun gear 351, planetary carrier 353that supports planetary gear 352, which is meshed with the sun gear 351,enabling the planetary gear 352 to be rotated around its axis, and thatis rotated by the orbital motion of the planetary gear 352, internalgear 354 meshed with the planetary gear 352, and planetary housing 360connected with the second side 332 of the center section 330 so as toenclose these gears.

Of three elements of the planetary gear unit 350, that is, the sun gear351, the planetary carrier 353 and the internal gear 354, first andsecond elements are respectively connected with the input shaft 301 andthe output shaft 302 of the HST 300, while running power to betransmitted to the driving wheels is taken off from a third element.

In this embodiment, the planetary carrier 353, the sun gear 351 and theinternal gear 354 respectively correspond to the first to thirdelements.

In this embodiment, the planetary gear unit 350 is provided with PTOoutput shaft 371 and running-power output shaft (HMT output shaft) 372respectively disposed coaxial with the HST input shaft 301 and the HSToutput shaft 302. The PTO output shaft 371 is supported by the planetaryhousing 360 so as to have an upstream end connected with the HST inputshaft 301 in a non-rotatable manner around the axis, and a downstreamend protruding from the planetary housing 360 to the downstream side.

More specifically, the planetary housing 360 includes end wall portion361 on the downstream side (a rear wall portion in this embodiment) andperipheral wall portion 362 extending upstream from a peripheral edge ofthe end wall portion 361, and has an upstream side (a forward side inthis embodiment), which is opened to the outside. Integrally formed withthe peripheral wall portion 362 of the planetary housing 360 is bossportion 363, which radially inwardly extends from an inner peripheralsurface of the peripheral wall portion 362. Bearing plate 364 isattached to the boss portion 363 via screws.

The PTO output shaft 371 is rotatably supported by the bearing plate 364and the end wall portion 361 so as to have an upstream end protrudingupstream from the bearing plate 364 and a downstream end protrudingdownstream from the end wall portion 361. The upstream end of the PTOoutput shaft 371 is provided with a spline coupling, into which thedownstream end of the input shaft 301 relatively non-rotatablyprotrudes.

Also, supported on the bearing plate 364 is running-power intermediateshaft 373 disposed coaxial with the HST output shaft 302 and connectedwith the HST output shaft 302 in such a manner as to be relativelynon-rotatable around its axis. The running-power intermediate shaft 373has an upstream end that is provided with a spline coupling, into whichthe downstream end of the HST output shaft 302 relatively non-rotatablyprotrudes. A portion of the running-power intermediate shaft 373, whichis located on the downstream side of the bearing plate 364, is providedwith the sun gear 351 serving as the second element.

Transmission gear 381 is relatively rotatably supported on a portion ofthe running-power intermediate shaft 373, which is located on thedownstream side of the bearing plate 364. The transmission gear 381constitutes a part of gear train 380 which operatively connect the PTOoutput shaft 371 or the HST input shaft 301 and the planetary carrier353 serving as the first element. Specifically, fixed gear 382 isrelatively non-rotatably supported on a portion of the PTO output shaft371, which is located on the downstream side of the bearing plate 364,so as to be meshed with the transmission gear 381. The planetary carrier353 is connected with the transmission gear 381 so as to enable theplanetary gear 352 to orbit around the sun gear 351 by the rotation ofthe transmission gear 381.

The running-power output shaft 372 has an upstream end relativelynon-rotatably connected with the internal gear 354 serving as the thirdelement, and a downstream end relatively rotatably supported on the endwall portion 361 so as to protrude downstream from the planetary housing360. The running-power output shaft 372 serves as the HMT output shaft.

With the above arrangement, a simplified assembling operation, whichinvolves only attaching the upstream opening of the planetary housing360 to the second side 332 of the center section 330 after assemblingthe planetary gear unit 350, enables operative connection of theplanetary carrier 353 with the HST input shaft 301, operative connectionof the sun gear 351 with the HST output shaft 302, and taking off of thePTO drive power having a constant speed of rotation and therunning-power having a variable speed of rotation respectively throughthe downstream ends of the PTO output shaft 371 and the running-poweroutput shaft 372.

As described above, in this embodiment, the HMT, which is made up by thecombination of the HST 300 and the planetary gear unit 350, is employedas the main-speed change unit 30 arranged in the running-powertransmission path. Thus, it is possible to widen the speed change rangeof the output of the HST while not causing increase in volume of theHST, and omit the necessity to provide a sub-speed change unit to bearranged in the running-power transmission path, or minimize the speedchange range of a provided sub-speed change unit so as to reduce thenumber of speed stages at the sub-speed change unit.

FIG. 5 illustrates the relationship between the slant angle of theoutput adjustment member 313 in the HST 300 (the movable swash plate inthis embodiment) and the rotational speed of the HMT output shaft (therunning-power output shaft 372 in this embodiment).

As illustrated in FIG. 5, the HMT 30 of this embodiment is so designedas to be held in a substantially output shutdown mode during the HST 300is at a maximum output level in either forward or reverse direction (thereverse rotation in FIG. 5), while being held in a maximum output modeduring the HST 300 is at a maximum output level in the oppositedirection (the forward rotation in FIG. 5). That is, the HMT 30 is onlycapable of driving the running-power output shaft 372 from 0 to themaximum speed of the vehicle by the rotation in a single direction, thusavoiding increase in size of the HST 300. The travel direction of thevehicle is changed from forward to reverse or vice versa by a laterdescribed geared forward/reverse travel direction changing unit, therebyexpanding twice the running speed change range covering the forwardtravel and the reverse travel of the vehicle.

With the above arrangement, even where the output of the HST outputshaft 302 is zero (that is, the HST 300 is held in a neutral mode),running power is outputted from the HMT 30. Therefore, during the outputadjustment member 313 (the movable swash plate) of the HST 300 is heldin the neutral mode, the power transmission path from the engine to thedriving wheels can be kept in a condition in which drive power ismechanically transmitted with high efficiency.

Now, the description will be made for a mounting structure of the HMT30.

The HMT 30 is fixedly connected with the engine 20 which is supported tothe vehicle frame 10 in vibration free manner, thereby constitutingalong with the engine 20 a driving-side unit which can be freelyvibrated against the vehicle frame 10.

That is, the driving-side unit constituted by the connection of theengine 20 with the HMT 30 is supported via rubber cushions 111 to fourrubber-cushioned brackets 11 d, which are secured to the pair of mainframes 11 closer to the front side of the pair of main frames 11 withspacing from each other in the fore and aft direction of the vehicle,and each two of the four brackets being located on each lateral side ofthe vehicle frame.

More specifically, the part of the engine 20 of the driving-side unit issupported on the rubber-cushioned brackets 11 d via brackets 20 asecured to the opposite lateral sides of the crank case closer to frontlower side and the rubber cushions 111.

On the other hand, the part of the HMT 30 of the driving-side unit issupported on the rubber-cushioned brackets 11 d via brackets 30 asecured to the opposite lateral sides of the planetary housing 360 andrubber cushions (not shown), as illustrated in FIG. 3.

The vibration free support of the driving-side unit relative to thevehicle frame can effectively prevent vibration of the engine 20, andvibration of the HST itself due to pulsation of working fluidcirculating within the HST 300 or any other causes from transmitting tothe vehicle frame 10, hence preventing deterioration in ride quality dueto the thus generated vibration.

Specifically, the HMT 30 is connected with the engine 20 via HMTmounting member 80, which includes mounting flange 81 attached to therear side of the crank case of the engine 20 and HMT mounting block 82attached to the mounting flange 81.

The HMT mounting block 82 includes four legs 83 extending upright fromthe mounting flange 81, and vertically oriented side portion 84extending between downstream ends of the legs 83. The four legs 83 arearranged so as to have the outer circumference of the flywheel 60exposed to the outside from a phantom line that connects the adjacentlegs. Thus, in this embodiment, instead of a conventional flywheelhousing, which is of the type that entirely covers the flywheel 60, theHMT mounting block 82 is used so as to minimize the distance between thepair of main frames 11 in the width direction thereof.

The vertically oriented side portion 84 is provided with mounting flange85, which forms a central opening, which allows the HST input shaft 301to be inserted therethrough and the charge pump unit 70 to be placedtherein. A front wall of the HST case 340 is attached to the mountingflange 85.

Now, the description will be made for the transmission 40.

The transmission 40 includes transmission case 410, running-power inputshaft 401 supported by the transmission case 410 so as to have anupstream end extending outwards, running-power output shaft 402 foroutputting drive power to the front wheels and/or rear wheels, and wheeldrive train 420 for transmitting drive power from the running-powerinput shaft 401 to the running-power output shaft 402, as illustrated inFIG. 2.

FIG. 6 is an exploded perspective view of the vehicle frame 10 and thetransmission 40. As illustrated in FIGS. 1 and 6, the transmission case410 is fixedly supported on the pair of main frames 11 closer to thesecond side of the fore and aft direction of the vehicle with a distancefrom the driving side unit. On the opposite lateral sides of thetransmission case 410 are provided rear axle housings 450, each of whichcontains axle brake unit 451 (see FIGS. 2 and 6).

Preferably, the rear axle housings 450 have an identical structure so asto be applicable to the opposite lateral sides of the transmission case410. In this embodiment, each rear axle housing 450 is provided withbosses 452 on upper and lower portions of its lateral side forsupporting brake arm 451, which is to control a corresponding one of thebrake units 451, and on top and bottom sides with mounting bosses 453for mounting to the pair of main frames 11 (see FIG. 6).

Reference numeral 411 in FIG. 6 represents a mounting boss formed on theopposite lateral sides of the transmission case 410 closer to the frontend thereof for mounting to the pair of main frames 11. Referencenumerals 11 e in FIG. 6 represent transmission mounting bracketsrespectively secured to the opposite outer sides of the pair of mainframes 11 closer to the rear ends thereof so as to be placed and securedto upwardly facing ones of the mounting bosses 453 of the rear axlehousing 450.

The running-power input shaft 401 is operatively connected with therunning-power output shaft 372 of the planetary gear unit 350 via shaftcoupling 91, which extends along the fore and aft direction of thevehicle as slanting downward towards the rear side. Preferably, avibration absorbing coupling with universal joints provided at theopposite ends is employed as the shaft coupling 91.

The wheel drive train 420 includes forward/rearward travel directionchanging unit 430 for changing the output direction (rotationaldirection) of the running-power output shaft 402 relative to therunning-power input shaft 401. More specifically, the wheel drive train420 includes a power transmission path for the forward travel, whichtransmits power during the forward travel, and a power transmission pathfor the rearward travel, which transmits power during the rearwardtravel. The forward/rearward travel direction changing unit 430 includesa hydraulically actuated clutch so as to be capable of being shifted toa forward travel position for selecting the power transmission path forthe forward travel (that is, a mode enabling direct engagement of drivenshaft 431 with the running-power input shaft 401), a rearward travelposition for selecting the power transmission path for the rearwardtravel (that is, a mode enabling engagement between the running-powerinput shaft 401 and the driven shaft 431 via an idle gear), and afreewheel position for shutting off both the power transmission paths ofthe wheel drive train 420 (that is, a mode shutting off the powertransmission relationship between the HMT output and the driving wheels)and bringing the driving wheels into freewheel state.

In this embodiment, although the wheel drive train 420 is provided withtwo-speed geared sub-speed change unit 440 between the driven shaft 431of the forward/rearward travel direction changing unit 430 and therunning-power output shaft 402, this sub-speed change unit can beomitted in case where the main-speed change unit (HMT) can outputrunning power with its speed change range covering the regular speed ofthe vehicle.

Thus, the working vehicle of this embodiment, in which the driving-sideunit is constituted by connecting the HMT 30 serving as the main-speedchange unit with the engine 20, which is supported on the vehicle frame10 closer to the first side of the fore and aft direction of the vehiclein vibration free manner; the transmission case 410 is fixedly supportedon the vehicle frame 10 closer to the second side of the fore and aftdirection of the vehicle with a distance from the driving-side unit; andthe running-power output shaft (HMT output shaft) 372 of the planetarygear unit 350 is connected with the running-power input shaft 401 of thetransmission 40 via the shaft coupling 91, secures a free spacesubstantially in the center of the vehicle frame 10 with respect to thefore and aft direction of the vehicle without expanding the vehiclelength. The free space thus secured achieves improved design flexibilityfor arranging such as a step bar or board of the driver's seat and amid-mount mower.

If the shaft coupling 91 is designated as being of a vibration absorbingtype, it is possible to securely achieve power transmission from thedriving-side unit to the transmission 40, while more effectivelypreventing vibrations of the driving-side unit from transmitting to thetransmission 40.

Reference numeral 403 in FIGS. 2 and 6 represents afront-wheel-driving-power-take-off-shaft, which is operatively connectedvia a clutch with the running-power output shaft 402 so as to be capableof turning on and off transmission of power and is connected via shaftcoupling 94 extending towards the front side of the vehicle frame withfront axle unit 90 suspended by a portion of the vehicle frame 10 closerto the front side thereof Reference numeral 50 in FIG. 2 represents adifferential gear unit operatively connected with the running-poweroutput shaft 402 for connecting the right and left rear wheels together,enabling the wheels to revolve at different speeds.

In this embodiment, the transmission 40 further includes PTO input shaft405 supported on the transmission case 410 so as to have an upstream endextending outwards, drive train 460 for taking off drive power for theworking implement (hereinafter referred to as “working-implement PTOdrive train”) 460, which transmits drive power inputted into the PTOinput shaft 405, rear-PTO shaft 406 protruding rearwards of the vehicle,mid-PTO shaft 407 running under the vehicle, and sub-pump unit 480.

The PTO input shaft 405 is operatively connected with the PTO outputshaft 371 of the planetary gear unit 350 via shaft coupling 92, whichextends along the fore and aft direction of the vehicle as slantingdownward towards the rear side. With this arrangement, the workingvehicle 1 of this embodiment can secure a free space substantially inthe center of the vehicle frame 10 with respect to the fore and aftdirection of the vehicle without expanding the vehicle length, althoughit is provided with the drive train for the working implement.

Preferably, the shaft coupling 92 is designated as being of a vibrationabsorbing type, which includes universal joints at the opposite ends,thereby more effectively preventing vibrations of the drive-side unitfrom transmitting to the transmission 40.

The working-implement PTO drive train 460 includes sub-pump-unit-drivegear train 465 for transmitting power from the PTO input shaft 405 tothe sub-pump unit 480, hydraulic PTO clutch unit 470 for engaging anddisengaging power from the PTO input shaft 405 to the mid-PTO shaft 407and the rear-PTO shaft 406 in an area downstream of thesub-pump-unit-drive gear train 465, and switching mechanism 475 forselectively switching the power transmission path of drive powertransmitted from the PTO input shaft 405 to the mid-PTO shaft 407 only,the rear-PTO shaft 406 only, or both the mid-PTO shaft 407 and therear-PTO shaft 406 in an area downstream of the hydraulic PTO clutchunit 470.

The drive power transmission path of the rear-PTO shaft 406 is providedwith two-speed rear PTO speed change unit 476 on the downstream side ofthe switching mechanism 475. As illustrated in FIG. 6, thefront-wheel-driving-power-take-off-shaft 403 and the mid-PTO shaft 407respectively have outward extensions extending from the front lower sideof the transmission case so as to be disposed in lateral side-by-siderelationship. The mid-PTO shaft 407 is connected with a mower attachedto the bottom of the vehicle via shaft coupling 93.

The sub-pump unit 480 is driven by the sub-pump-unit-drive gear train465 located on the upstream side of the hydraulic PTO clutch unit 470,as described above. Therefore, the sub-pump unit 480 is constantlydriven when the engine runs.

FIG. 7 is a hydraulic circuit diagram of the sub-pump unit 480.

The sub-pump unit 480 is located on the transmission case 410, asdescribed above, and is in an integral relationship with the vehicleframe 10. Accordingly, the sub-pump unit 480 does not serve as ahydraulic source for the HST 300, which is integrally vibrated with theengine, but a hydraulic source for hydraulic equipment, which is in anintegral relationship with the vehicle frame 10.

That is, the sub-pump unit 480 serves as a hydraulic source forfront-wheel power steering unit 110 provided in the vehicle according todesire or need, the hydraulic PTO clutch unit 470 equipped with anegative brake mechanism, the forward/rearward travel direction changingunit 430, hydraulic lift unit 120 provided in the vehicle according todesire or need in order to lift the working vehicle attached to the rearside of the vehicle, hydraulic supply unit 130 of a front loader Fequipped on the front side of the vehicle according to desire or need,and the like.

In this embodiment, pressurized hydraulic fluid supplied from thesub-pump unit 480 is first supplied to the front-wheel power steeringunit 110 and drain fluid therefrom is then divided into theforward/rearward travel direction changing unit 430 and other hydraulicequipment by means of a flow dividing valve. In this regard, it is to benoted that the hydraulic circuit of the present invention is notnecessarily limited to this, but rather it can take variousarrangements.

Now, the description will be made for the vehicle frame 10 of theworking vehicle according to this embodiment.

The vehicle frame 10 includes the pair of main frames 11 extending inthe fore and aft direction of the vehicle on the opposite lateral sidethereof, as described above. As illustrated in FIG. 6, the pair of mainframes 11 respectively have first horizontal portions 11 a, slantingportions 11 b slanting upward from the first ends in the fore and aftdirection of the vehicle (the rear ends in this embodiment), secondhorizontal portions 11 c which extend horizontally from the first endsof the slanting portions 11 b in the fore and aft direction of thevehicle (the rear ends in this embodiment), thus forming a substantiallyZ-shape as viewed from the lateral side (or substantially reverseZ-shape). The slanting portions 11 b and the second horizontal portions11 c are placed over the connected member comprising the transmissioncase 410 and the rear axle housing 450 so as to support the connectedmember, in which the connected member also serves as a cross member forthe pair of main frames.

The vehicle frame 10 further includes reinforcing frame 12 having agate-like shape and connected between the pair of main frames 11. Inthis arrangement, the reinforcing frame 12 also serves as a crossmember. The reinforcing frame 12 is preferably disposed substantially inthe center of the first horizontal portions 11 a in the fore and aftdirection thereof to straddle over the flywheel 60, the HST 300 and thelike.

More specifically, the reinforcing frame 12 has a pair of lateral sidewall portions 12 a respectively connected with the pair of main frames11, and top wall portion 12 b extending between the pair of lateral sidewall portions 12 a. Front loader masts 131 are attachable to upperportions of the opposite lateral side wall portions 12 a. Substantiallyin the lateral center of the top wall portion 12 b is provided pedestal12 c for installing controller 110 a for the front-wheel power steeringunit 110, handle column Sa for supporting handle S, and the like.Further, it is possible to provide a stay secured to the reinforcingframe 12 so as to enable peripheral parts such as a dashboard panel tobe attached to the frame. The reinforcing frame 12 is made of a steelplate in this embodiment but may be made from cast metal when thebending strength is to be increased.

The vehicle frame 10 further includes top plate 13 disposed straddlingover top sides of the pair of main frames 11 so as to serve as a crossmember. The top plate 13 is designed to be capable of suspending andsupporting the hydraulic lift unit 120, and preferably located above andin proximity with the transmission 40. In this embodiment, the top plate13 is disposed straddling over the top sides of the second horizontalportions 11 c of the pair of main frames 11.

Now, the description will be made for the hydraulic lift unit 120 and asupporting structure of the hydraulic lift unit 120 by the top plate 13.FIGS. 8 and 9 are respectively plan and side views of the hydraulic liftunit and its proximity with parts illustrated in cross section.

As illustrated in FIGS. 6, 8 and 9, the hydraulic lift unit 120 includesmounting member 121 secured to the top plate 13, single-action ordouble-action hydraulic cylinder 122 pivotally supported by the mountingmember 121, hydraulic piston 123 placed in the hydraulic cylinder 122 soas to be capable of reciprocally moving by the effect of hydraulicpressure, and a pair of lift arms 124 operatively connected with apiston rod of the hydraulic piston 123.

More specifically, the mounting member 121 has top side 121 a attachedto a bottom surface of the top plate 13, and lateral side wall portions121 b extending downward from the opposite ends of the top side 121 a ina vehicle width direction, thus having a U-shape in cross section. Themounting member 121 is formed such as by bending a steel plate. Liftcontrol valve 120 a of the hydraulic lift unit 120 is attached to theouter side of one of the lateral side wall portions 121 b. The liftcontrol valve 120 a is provided with pump port 120 b for receiving drainfluid from the front-wheel power steering unit 110, and cylinder port120 c for supply and discharge of pressurized hydraulic fluid for thehydraulic piston 123 of the hydraulic lift unit 120.

Front-side cross bar 121 c supported on the lateral side wall portions121 b is located on the front side of the mounting member 121. Thehydraulic cylinder 122 is pivotally supported on the front-side crossbar 121 c so as to be positioned between the lateral side wall portions121 b. Rear-side cross bar 121 d supported on the lateral-side wallportions 121 b is located on the rear side of the mounting member 121.The rear-side cross bar 121 d has opposite ends respectively extendingoutwards from the lateral side wall portions 121 b of the mountingmember 121, and the pair of lift arms 124 are pivotally supported onthese opposite ends.

As illustrated in detail in FIGS. 8 and 9, the pair of lift arms 124 hasa substantially V-shape as viewed from the lateral side. Morespecifically, the pair of lift arms 124 respectively have first pieces124 a each having a first end pivotally supported on the rear-side crossbar 121 d and a second end extending forward and downward from the firstend, and second pieces 124 b extending rearward from the second ends ofthe first pieces 124 a.

Connection bar 124 c is provided for connection between the second ends(apex ends) of the first pieces 124 a in the pair of lift arms 124, andthe piston rod is connected with the connection bar 124 c substantiallyat its center in the vehicle width direction. Lift link 150, which isconnected with a lower link, a constitutional element of a conventionalthree-point link hitch mechanism, is at its upper end attached to therear ends of the second pieces 124 b. The mounting member 121 isprovided at the rear end with hinge 151, to which a top link of thethree-point link hitch mechanism is attached.

In FIG. 9, reference numeral 122 a represents a fluid supply/dischargeport of the hydraulic cylinder 122, which port is connected with thecylinder port 120 c of the lift control valve 120 a via conduit.Reference numeral 122 b represents air/leaked fluid drain port of thehydraulic cylinder 122 in an arrangement with the hydraulic cylinder 122being designated as being of a single action type, which port beingconnected with an upper air reservoir of the transmission case 410 viaconduit.

The above described arrangement of this embodiment, in which the topplate 13 with the hydraulic lift unit 120 attached thereto is detachablysecured to the top sides of the pair of main frames 11, produces thefollowing desirable effects.

According to the above arrangement, load generated by lifting theworking implement by the hydraulic lift unit 120 is not applied to thetransmission case 410 but applied directly to the pair of main frames11. As a result, it is not necessary to manufacture the transmissioncase 410 with an increased strength. Also, the top plate 13, whichconnects the pair of main frames 11 together, serves as a cross member.

In addition, the above arrangement achieves ease of replacement ormaintenance of the hydraulic lift unit 120, as well as ease ofassembling, since the hydraulic lift unit 120 is previously attached tothe top plate 13 so as to have a pre-assembled unit, which can beinstantly attached to and detached from the pair of main frames 11. Forexample, the replacement of the hydraulic cylinder with a high or lowvolume hydraulic cylinder can be made on a unit-by-unit basis, whichmeans the pre-assembled unit is entirely replaced with a new oneconstituted by a top plate with a different volume hydraulic cylinderattached thereto without the necessity of paying attention to otherparts such as a transmission case.

The vehicle frame 10 is further provided at its first end in the foreand aft direction of the vehicle (the rear end in this embodiment) withsupport frame 14, which connects between the pair of main frames 11 inorder to support a ROPS (Roll-over Protection System).

The ROPS support frame 14 includes a pair of vertical extensions 14 arespectively connected with the rear ends of the second horizontalportions 11 c of the pair of main frames 11 and upper plate 14 b forconnection between upper ends of the pair of vertical extensions 14 a sothat ROPS 140 can be mounted on the upper plate 14 b. The pair ofvertical extensions 14 a may be designed to be capable of supportingthereon lower-link pivotably supporting bar 14 c, which extends betweenthe pair of vertical extensions 14 a (see FIGS. 1 and 6).

The vehicle frame 10 may include bottom plate 15 for connection betweenlower ends of the pair of vertical extensions 14 a in the ROPS supportframe 14. This bottom plate 15 forms a rectangular reinforcing frame incooperation with the ROPS support frame 14, thereby increasing rigidityof not only the ROPS support frame 14 but also the vehicle frame 10connected thereto.

Preferably, a tow-bar storage box 15 a for supporting a tow bar isattached to the bottom side of the bottom plate 15.

In this embodiment, the bottom plate 15 has a top side to which thetransmission case 410 is secured in an attempt to further improve therigidity of the ROPS support frame 14 and the vehicle frame 10, as wellas securely support the transmission case 410.

Now, the description will be made for a speed-change control mechanismof the working vehicle 1 according to this embodiment. A speed-changecontrol circuit diagram of the working vehicle is illustrated in FIG.10.

As illustrated in FIG. 10, the speed-change control mechanism of theworking vehicle 1 includes forward pedal 510 and back pedal 520,speed-adjusting hydraulic assembly 530 for controlling the slant angleof the output adjustment member 313 of the HST 300, travel-directionchanging hydraulic assembly 540 for controlling the forward/rearwardtravel direction changing unit 430, and control unit 550 forcomprehensively controlling the respective units.

The control unit 550 includes control part 551 such as a CPU, and sensorpart 552 for detecting and sensing the operational state of each unit ormember. In this embodiment, the sensor part 552 includes operationdetection sensor 552 a for detecting whether each of the forward pedal510 and the back pedal 520 is under operation based upon the presence orabsence of the rotation of a corresponding pedal shaft, operation amountdetection sensor 552 b such as a potentiometer for detecting therotational travel distance of the pedal shaft of each pedal (a depressedpedal angle), slant angle detection sensor 552 c for detecting the slantangle of the output adjustment member 313 of the HST 300, HST inputsensor 552 d for detecting the rotational speed of the input shaft 301of the HST 300 or the PTO output shaft 371 directly connected with thisHST input shaft 301, and HST output sensor 552 e for detecting therotational speed of the HST output shaft 302.

The fact whether each of the pedals 510 and 520 has been operated (ordepressed) can also be detected based upon the fact whether a signalother than a signal representative of an initial value has been sentfrom the operation amount detection sensor 552 b. That is, the time atwhich a signal other than the signal representative of an initial valuehas been sent from the operation amount detection sensor 552 b can beregarded as the time at which either of the pedals 510, 520 has beenoperated. This arrangement can omit the operation detection sensor 552a. The respective pedals are mounted along with return springs (notshown) so that the detection value sent from the respective sensors 552can be set at zero when the driver has removed the driver's foot from acorresponding pedal.

The speed-adjusting hydraulic assembly 530 includes hydraulic pistonunit 531 including a piston operatively connected with the outputadjustment member 313 of the HST 300, and solenoid proportional controlvalve 532 for switching a hydraulic-fluid supply/discharge passage, inwhich the slant angle of the output adjustment member 313 can be changedor held in the current angle by switching the hydraulic-fluidsupply/discharge passage.

That is, a valve body of the solenoid proportional control valve 532 isdesigned to be capable of taking a first position enabling the HST 300to have its output with the rotational direction shifted to eitherforward and reverse direction, a second position enabling the HST 300 tohave its output with the rotational direction shifted to the oppositedirection, and a neutral position enabling the HST 300 to have itsoutput held in the current state.

As illustrated in FIG. 10, the solenoid proportional control valve 532receives pressurized hydraulic fluid from the charge pump unit 70.Therefore, the solenoid proportional control valve 532 is preferablymounted in the drive-side unit along with the hydraulic piston unit 531.

The travel-direction changing hydraulic assembly 540 includes solenoiddirectional control valve 541 for changing a hydraulic-fluidsupply/discharge passage of the forward/rearward travel directionchanging unit 430 so as to be capable of changing the rotationaldirection of the running-power output shaft 402 of the transmission 40from forward to reverse or vice versa, as well as shutting off the powertransmission path to the running-power output shaft 402.

That is, a valve body of the solenoid directional control valve 541 isdesigned to be capable of being shifted to a forward travel positionapplying pressurized hydraulic fluid to the forward/rearward traveldirection changing unit 430 thus enabling the engagement of the powertransmission path for the forward travel, a rearward travel positionapplying pressurized hydraulic fluid to the forward/rearward traveldirection changing unit 430 thus enabling the engagement of the powertransmission path for the rearward travel, and a neutral positionshutting off the power transmission path of the wheel drive train 420.The solenoid directional control valve 541 receives pressurizedhydraulic fluid from the sub-pump unit 480.

The thus arranged speed change control mechanism is operated in thefollowing manner.

As described above, the HMT 30 is held in the substantially outputshutdown mode during the output adjustment member 313 of the HST 300 isslanted to the maximum slant angle (hereinafter referred to as “initialangle”) in either forward or reverse directions and gradually increasesits output as the output adjustment member 313 is slanted in theopposite direction.

In the working vehicle 1 of this embodiment, the above relationshipbetween the output adjustment member 313 and the output of the HMT canbe achieved by the following structure.

When the vehicle is stopped with the engine 20 still running and bothpedals 510, 520 being out of operation, each sensor 552 detects a valueof zero which is then inputted into the control part 551. Based upon theinputted signals, the control part 551 shifts the solenoid proportionalcontrol valve 532 to the first position, thereby allowing thespeed-adjusting hydraulic assembly 530 to press the output adjustmentmember 313 toward the initial angle. Once the output adjustment member313 is detected as having been reached the initial angle, the controlpart 551 returns the solenoid proportional control valve 532 to theneutral position.

At this moment, the setting of the initial angle of the outputadjustment member 313 is adjusted by the calculation of the control part551 based upon detected signals from the HST input sensor 552 d and theHST output sensor 552 e in addition to signals from the slanting angledetection sensor 552 c. That is, since the rotational speedsrespectively inputted into the sun gear 351 and the planetary carrier353 can be found based upon signals of the HST output sensor 552 e andthe HST input sensor 552 d, the fact whether the HMT 30 is held in thesubstantially output shutdown mode can be confirmed by the calculationbased upon the set gear ratio of the planetary gear unit 350.

In this embodiment, by the calculation based upon the rotational speedof the HST input shaft 301 and the rotational speed of the HST outputshaft 302, a zero power output of the HMT can be confirmed.Alternatively to this, it is possible to provide the HMT output shaft(the running-power output shaft) 372 with a rotation speed sensor. Inthis regard, it is to be noted that when comparing two differentdetection manners for detecting the substantially output shutdown modeof the HMT 30, one made by the rotational speed sensor based upon itsdetected rotational speed of the HMT output shaft 372, and another madeby the calculation based upon the rotational speed of the HST inputshaft 301 and the rotational speed of the HST output shaft 302, theanother one causes less detection error. Therefore, the non-rotation ofthe HMT output is preferably detected by the calculation based upon therotational speed of the HST input shaft 301 and the rotational speed ofthe HST output shaft 302.

Now, the description will be made for the operation to move the workingvehicle 1 forward and rearward.

In order to move the working vehicle forward or rearward, the driverselectively presses either the forward pedal 510 or the back pedal 520.For example, assuming that the driver presses the forward pedal 510, thecontrol part 551 detects the start of the pedal operation based uponinputted signals from the operation detection sensor 552 a or theoperation amount detection sensor 552 b, and then shifts the valve bodyof the solenoid directional control valve 541 of the travel-directionchanging hydraulic assembly 540 to the forward travel position. Whereby,the forward/rearward travel direction changing unit 430 is switched intoa forward travel mode enabling engagement of the power transmission pathfor the forward travel.

As the driver depresses the forward pedal 510 further, the control part551 controls the solenoid proportional control valve 532 based uponinputted signals from the operation amount detection sensor 552 b, theslanting angle detection sensor 552 c, the HST input sensor 552 d andthe HST output sensor 552 e so as to allow the operational amount of theforward pedal 510, the slant angle of the output adjustment member 313and the HMT output to have the relationship as shown in FIG. 5.

When the driver has removed pressure from the forward pedal 510 therebyreleasing the same from the operational mode, the control part 551controls the solenoid directional control valve 541 to be held in thecurrent state (that is, a state enabling the valve body of the solenoiddirectional control valve 541 to be held in the forward travel position.

That is, during the driver presses the forward pedal 510 into theoperational mode, the control part 551 excites forward-travel excitedsolenoid 541 a of the solenoid directional control valve 541 to have thevalve body of the solenoid directional control valve 541 held in theforward travel position. When the driver has removed pressure from theforward pedal 510 and released the same from its depressed state, thecontrol part 551 controls the solenoid directional control valve 541 tokeep the forward-travel excited solenoid 541 a in its excited state.

According to the above arrangement, even when the forward pedal 510 hasbeen taken out of the operational mode, that is, a depressed state whilethe vehicle travels forward by pressing the forward pedal 510, the powertransmission path for the forward travel is held in the engaging state.

Meanwhile, when the forward pedal 510 has been released from theoperational mode or depressed state, the HST 300 is changed into themaximum output mode in either forward or reverse direction, while theHMT is forced into a zero output shutdown mode. That is, taking theforward pedal 510 out of the operational mode causes the driving wheelsto be brought into operative connection with the running-power outputshaft 372, which has been forced into a zero output mode. Whereby, thebraking force effected by the HMT 30 is applied to the driving wheels.The braking force of the HMT acts as a resistance force against therotation of the driving wheels when the vehicle has been stopped, thuspreventing the vehicle to unintentionally move. The braking force of theHMT also acts on the driving wheels when the back pedal has beenreleased from its operational mode.

Thus, in the working vehicle 1 of this embodiment, when the forwardpedal 510 or the back pedal 520 has been drawn from an inoperative modeinto the depressed, operational mode, the forward/rearward traveldirection changing unit 430 engages a corresponding power-transmissionpath. On the other hand, when the forward pedal 510 or the back pedal520 has been released from the depressed, operational mode, theforward/rearward travel direction changing unit 430 holds thecorresponding power-transmission path in its engaged state. Whereby,when the working vehicle has been stopped, the braking force of the HMTis applied to the driving wheels.

Further, the working vehicle 1 of this embodiment includes freewheelmechanism 600 for forcing the forward/rearward travel direction changingunit 430 into the neutral mode when the HMT 30 is in the substantiallyoutput shutdown mode. More specifically, the freewheel mechanism 600includes operation member 601 such as an operation lever provided at thedriver's seat, and operation detection sensor 602 for detecting the ONand OFF positions of the operation member 601. With this arrangement,when an ON signal is inputted from the operation detection sensor 602into the control part 551 during the HMT 30 is in the substantiallyoutput shutdown mode, the control part 551 shifts the valve body of thesolenoid directional control valve 541 to the neutral position.

Once the valve body of the solenoid directional control valve 541 hasbeen shifted to the neutral position, pressurized hydraulic fluid in theforward/rearward travel direction changing unit 430 is drained, andpressurized hydraulic fluid from the charge pump unit 70 issimultaneously drained. Whereby, the power transmission path of thedrive train for the driving wheels is shut off. That is, shifting thevalve body of the solenoid directional control valve 541 to the neutralposition causes the driving wheels to be brought into a freewheel moderelative to the HMT output shaft 372.

The thus provided freewheel mechanism 600 allows the working vehicle tobe easily moved with the engine still running, when the working vehicleis to be forcibly towed or pressed forward or rearward. The fact whetherthe HMT 30 is in the substantially output shutdown mode can be detectedby the calculation of inputted signals from the HST input sensor 552 dand the HST output sensor 552 e.

The thus arranged working vehicle 1 produces the following desirableeffects.

In the power transmission path for the driving wheels, which extendsfrom the engine 20 to the driving wheels, the HMT 30 that is made up bythe combination of the HST 300 and the planetary gear unit 350, and theforward/rearward travel direction changing unit 430 that is connected intandem with the HMT 30 so as to operatively receive the output of theHMT 30 and change the rotational direction of the output of the HMT areinterposed. The HST 300 includes the hydraulic pump unit 310 and thehydraulic motor unit 320, at least one of which is designated as beingof the variable displacement type, the pump shaft 301 that isoperatively connected with the driving source 20 so as to drive thehydraulic pump unit 310, and the motor shaft 302 adapted to be driven bythe hydraulic motor unit 320. Also, the variable output of the HST(hereinafter referred to as “HST variable output”) in both the forwardand reverse directions is operatively inputted into the second elementof the planetary gear unit 350. The HMT 30 is so designed as to be heldin the substantially output shutdown mode during the HST variable outputis at the maximum level in either forward or reverse direction, andgradually shifted from the substantially output shutdown mode to themaximum output mode as the HST variable output is changed from themaximum output level in the either forward or reverse direction to themaximum output level in the opposite direction.

According to the above arrangement, the entire speed change rangeavailable by the HMT 30 can be applied to the speed change range for theforward travel or the speed change range for the rearward travel.Whereby, it is possible to decrease the size of the HST, while wideningthe speed change range covering both the forward and rearward travels(that is, the difference in absolute value between the maximum forwardtravel speed and the maximum rearward travel speed).

That is, in a conventional HMT, the forward and reverse rotations of theoutput of the HMT were achieved by a variable motor output of an HST.More specifically, in the conventional HMT, the output of the HMT inboth the forward and reverse directions is produced by changing thevariable motor output of the HST from the maximum output level in eitherforward or reverse direction to the maximum output level in the oppositedirection.

With the above conventional arrangement, it is necessary to increase thevolume of the HST in order to widen the running speed change rangecovering both the forward and rearward travels. The increased volume ofthe HST may invite high cost, increased size and weight of the entireHMT, and hence increased size of a cooling unit.

On the contrary to the above, in this embodiment, as described above,the entire speed change range of the output of the HMT, which isproduced by changing the HST variable output from the maximum outputlevel in either forward or reverse direction to the maximum output levelin the opposite direction, is taken off as the rotational output to theforward direction and the rearward direction, while the forward/rearwardtravel direction changing unit 430 is provided on the downstream side ofthe HMT so as to have the output of the HMT with the rotationaldirection changed in both the forward and reverse directions by theforward/rearward travel direction changing unit 430 and then transmitthe output to the driving wheels.

Therefore, of the running speed change range covering both the forwardand rearward travels, a range of which the HST is responsible for can benarrowed, thereby achieving downsizing of the HST. The downsizing of theHST can overcome the aforementioned disadvantages. In addition to that,when the HST 300 constitutes the drive unit with the engine as in thisembodiment, the downsizing of the HST 300 is advantageous in downsizingand light-weighting the drive unit, and contributes to a simplifiedvibration-free support structure for the drive unit.

Also, in the working vehicle 1 of this embodiment, the forward/rearwardtravel direction changing unit 430 is designed to be capable of beingswitched into a freewheel mode, which releases the driving wheels froman engaging relationship with the HMT by shutting off the powertransmission path for the driving wheels when the HMT 30 is in thesubstantially output shutdown mode.

The above arrangement omits the necessity to strictly control theprecision of the HMT in order to enable the HMT to solely obtain aprecise output shutdown mode, and hence achieves ease of manufacturingthe HMT. That is, in the conventional arrangement where the outputshutdown mode of the HMT is obtained based upon the slant angle of theoutput adjustment member of the HST, the HMT must be made with highprecision. Also, unless the HMT can be switched into the output shutdownmode only by the control of the output adjustment member of the HST, aclutch must be separately located on the downstream side of the HMT soas to shut off the running power transmission path.

On the contrary to the above conventional arrangement, in thisembodiment, the freewheel mode can be obtained by utilizing theforward/rearward travel direction changing unit 430 located on thedownstream side of the HMT 30, thus omitting the necessity to obtain aprecise output shutdown mode solely by the HMT. Therefore, the HMT 30can be relatively easily manufactured. Since the freewheel mode can beobtained by utilizing the forward/rearward travel direction changingunit 430, it is possible to produce the clutching function, whileminimizing the number of parts to be additionally prepared.

This embodiment is so constructed that the forward/rearward traveldirection changing unit 430 is switched into the freewheel mode when anoperating signal has been inputted from the outside via the operationmember 601. Alternatively to this, it is possible to employ thearrangement where the forward/rearward travel direction changing unit430 is automatically switched into the freewheel mode when the HMT 30has been switched into the substantially output shutdown mode.

FIG. 11 illustrates one example of a speed-change control circuit of theworking vehicle, which enables the forward/rearward travel directionchanging unit 430 to be automatically switched into the freewheel modewhen the HMT 30 has been switched into the substantially output shutdownmode. Hereinafter, the description will be made for the working vehicleas illustrated in FIG. 11 mainly with reference to differences relativeto this embodiment.

A speed-change control mechanism illustrated in FIG. 11 includes pedal510′ commonly used for the forward and rearward travels (hereinaftersimply referred to as “forward and back pedal”), forward/rearward traveldirection changing member 520′, the speed-adjusting hydraulic assembly530, the travel-direction changing hydraulic assembly 540, the controlunit 550 for comprehensively controlling the respective units, andfreewheel mechanism 600′.

The freewheel mechanism 600′ is designed to be capable of being switchedbetween a rotation-force application mode enabling rotation resistanceto be selectively applied and released relative to the members locatedon the downstream side of the forward/rearward travel direction changingunit 430, and a freewheel enabling mode enabling the driving wheels tobe brought into freewheel state.

More specifically, the freewheel mechanism 600′ includes operationmember 601′ provided at the driver's seat, ON/OFF sensor 602′ fordetecting ON and OFF of the operation member 601′, and hydraulic brakeunit 603′ capable of being switched into arotation-resistance-application mode when the operation member 601′ isheld in an OFF position and a rotation-resistance release mode when theoperation member 601′ is held in an ON position.

The hydraulic brake unit 603′ includes hydraulic piston 603 a′ adaptedto constantly apply braking force to the driven shaft 431 of theforward/rearward travel direction changing unit 430 by means of anurging member, and brake switching valve 603 b′ for switching ahydraulic fluid supply/discharge passage of the hydraulic piston, sothat the aforesaid rotation resistance is released when pressurizedhydraulic fluid has been supplied into the hydraulic piston 603 a′.

The brake switching valve 603 b′ is controlled by the control part 551in such a manner as to be securely held in a rotation-resistance releaseposition enabling pressurized hydraulic fluid to be supplied to thehydraulic piston 603 a′ when the operation member 601′ is held in the ONposition, and be capable of selectively taking the rotation-resistancerelease position and the rotation-resistance application position inassociation with the forward and back pedal 510′ and theforward/rearward travel direction changing member 520′ when theoperation member 601′ is held in the OFF position.

That is, when the operation member 601′ is held in the ON position, thehydraulic brake unit 603′ is held in the rotation-resistance releasemode, in which no braking force is applied irrespective of theoperational statuses of other operation members. On the other hand, whenthe operation member 601′ is held in the OFF position, the hydraulicbrake unit 603′ is held in the rotation-resistance-application mode, inwhich rotation resistance is selectively applied and released accordingto the operational statuses of the other operation members.

The thus arranged speed-change control mechanism is operated in thefollowing manner.

First, the description will be made for the case when the operationmember 601′ is held in the OFF position. When the forward and back pedal510′ is in the inoperative mode, the control part 551 controls thesolenoid directional control valve 541 and the hydraulic brake unit 603b′ so that the valve body of the solenoid directional control valve 541is held in the neutral position and the valve body of the brakeswitching valve 603 b′ is held in the rotation resistance applicationposition.

Once the driver shifts the forward/rearward travel direction changingmember 520′ to the forward travel position or the rearward travelposition, and then presses the forward and back pedal 510′, the controlpart 551 controls the solenoid directional control valve 541 and thebrake switching valve 603 b′ so as to shift the valve body of thesolenoid directional control valve 541 to the forward travel position orthe rearward travel position, and shift the brake switching valve 603 b′to the rotation-resistance release position, as well as controls thesolenoid proportional control valve 532 so as to produce the HMT outputcorresponding to the operation amount of the forward and back pedal510′. Whereby, it is possible to produce a vehicle running speedcorresponding to the operation amount of the forward and back pedal 510′in a direction selected by the forward/rearward travel directionchanging member 520′. The position detection of the forward/rearwardtravel direction changing member 520′ is performed based upon signalsfrom switching-member position sensor 552.

When the driver has removed pressure from the forward and back pedal510′, thus releasing the same from the operational mode, the controlpart 551 controls the solenoid proportional control valve 532 so as toswitch the HMT 30 into the substantially output shutdown mode, as wellas controls the solenoid directional control valve 541 and the brakeswitching valve 603 b′ so as to shift the valve body of the solenoiddirectional control valve 541 to the neutral position irrespective ofthe position of the forward/rearward travel direction changing member520′ and shift the brake switching valve 603 b′ to therotation-resistance application position.

That is, in the embodiment as illustrated in FIG. 11, assuming that theoperation member is held in the OFF position, when the driver starts thevehicle by shifting the forward/rearward travel direction changingmember 520′ into either the forward travel position or rearward travelposition and then pressing the forward and back pedal 510′, theforward/rearward travel direction changing unit 430 is switched into apower transmission mode and the hydraulic brake unit 603′ is switchedinto the rotation-resistance release mode.

Then, when the driver releases pressure from the forward and back pedal510′ so as to switch the HMT 30 into the substantially output shutdownmode, the forward/rearward travel direction changing unit 430 isswitched into the power shutdown mode and the hydraulic brake unit 603′is switched into the rotation-resistance-application mode in automaticmanner irrespective of the engaging position of the forward/rearwardtravel direction changing member 520′.

Now, the description will be made for the case when the operation member601′ is held in the ON position in the arrangement as illustrated inFIG. 11.

In the arrangement of FIG. 11, when the operation member 601′ is held inthe ON position, the control part 551 interprets it as “the driver hasdisplayed the driver's intention not to run the vehicle”, andautomatically switch the forward/rearward travel direction changing unit430 into the neutral mode based upon the substantially output shutdownmode of the HMT 30, irrespective of the operational status of theforward/rearward travel direction changing member 520′.

As described above, when the operation member 601′ is held in the ONposition, the hydraulic brake unit 603′ is held in therotation-resistance release mode. Accordingly, when the forward/rearwardtravel direction changing unit 430 is switched into the neutral mode,the driving wheels are brought into freewheel state, enabling themselvesto be freely rotated.

While this embodiment has been described by taking for example the casewhere the forward/rearward travel direction changing unit 430 is of ahydraulic clutch type, it is possible to employ forward/rearward traveldirection changing unit 430′, which is of either a collar shift type ora drag clutch type, as illustrated in FIG. 12.

In the embodiment illustrated in FIG. 12, the single solenoiddirectional control valve 541 is replaced by forward-travel switchingvalve 541F and rearward-travel switching valve 541R. Both the switchingvalves 541F, 541R respectively have output ports connected withhydraulic fluid input ports of outside-mounted, double-expansionhydraulic cylinder 700. With this arrangement, when both the switchingvalves 541F, 541R are held in pressurized-fluid supply position(position I in FIG. 12), the forward/rearward travel direction changingunit 430′ is switched into the neutral mode.

When the forward-travel switching valve 541F is held in thepressurized-fluid supply position (position I) and the rearward-travelswitching valve 541R is held in a pressurized-fluid discharge position(position II), the hydraulic cylinder 700 is contracted so as to shiftpiston 701 to the right hand side of the sheet, thereby switching theforward/rearward travel direction changing unit 430′ into the rearwardtravel mode.

On the contrary, when the forward-travel switching valve 541F is held inthe pressurized-fluid discharge position (position II) and therearward-travel switching valve 541R is held in the pressurized-fluidsupply position (position I), the hydraulic cylinder is expanded so asto shift the piston 701 to the left hand side of the sheet, therebyswitching the forward/rearward travel direction changing unit 430′ intothe forward travel mode. Reference numeral 702 in FIG. 12 represents aspring for constantly pressing clutch shifter 431′ to an engaging sideby storing operation force of the piston 701, in preparation forincomplete clutch engagement.

Second Embodiment

The description will be made for the second embodiment of the presentinvention with reference to the accompanied drawings. FIGS. 13 and 14are respectively a schematic side view of working vehicle 1′ accordingto this embodiment and a model view of the power transmission path.

In the following description, corresponding or identical parts to thoseof the first embodiment have been given the same reference characters orthose with primes (′) to omit a detailed description thereof.

As illustrated in FIG. 14, the working vehicle 1′ of this embodimentincludes the forward/rearward travel direction changing unit 430′interposed between the driving source 20 and the HMT 30 in place of theforward/rearward travel direction changing unit 430 provided within thetransmission 40 in the first embodiment.

Specifically, the working vehicle 1′ includes the vehicle frame 10, theengine 20 supported on the vehicle frame 10 closer to the first sidethereof relative to the fore and aft direction of the vehicle invibration free manner, the HMT 30 serving as a main-speed change unitfor changing the speed of drive power from the engine and transmittingthe same to a downstream member, transmission 40′ for driving the driveaxle upon receiving output of the HMT 30, and the forward/rearwardtravel direction changing unit 430′ interposed between the drivingsource 20 and the HMT 30.

FIG. 15 is a longitudinal cross-sectional side view of the HMT 30 andits proximity in the working vehicle 1′.

As illustrated in FIGS. 14 and 15, the forward/rearward travel directionchanging unit 430′ includes drive shaft 435′ connected with the flywheel60 preferably via damper 61, driven shaft 436′ located substantially inparallel with the drive shaft 435′, forward-travel power transmissionpath 430F′ for transmitting power from the drive shaft 435′ to thedriven shaft 436′ when in the forward travel, rearward-travel powertransmission path 430R′ for transmitting power from the drive shaft 435′to the driven shaft 436′ when in the rearward travel, and hydraulicallyactuated clutch 437 interposed between the forward-travel powertransmission path 430F′ and the rearward-travel power transmission path430R′.

In this embodiment, the forward/rearward travel direction changing unit430′ is placed within flywheel housing 65 located between the engine 20and the HST case 340.

That is, the working vehicle 1′ includes the flywheel housing 65′ inplace of the HMT mounting member 80. The flywheel housing 65′ includeshollow body 66′ having an upstream side connected with the mountingflange 81 and a downstream side connected with the HST case 340, andbearing wall 67′ provided substantially in the center area of the hollowbody 66′ in the power transmission direction. The hollow body 66′ has anupstream open end for receiving the flywheel 60 and a downstream openend for receiving the forward/rearward travel direction changing unit430′.

In the thus arranged flywheel housing 65′, the hollow body 66′ defines adry flywheel housing and a fluid-filledforward/rearward-travel-direction-changing-unit housing respectively inthe upstream side and the downstream side thereof with the bearing wall67′ therebetween. In this embodiment, the charge pump unit 70 is placedwithin the flywheel housing in such a manner as to be rotatable by thedrive shaft 435′. It is to be noted that the charge pump unit 70 can bedriven by any other shaft, or any other pump can also be functioned asthe charge pump.

The drive shaft 435′ is bearing-supported by the bearing wall 67′ andthe planetary housing 360. The drive shaft 435′ has an upstream endextending through the bearing wall 67′ and connected with the flywheel60, and a downstream end extending downstream through the center section330 and the planetary housing 360. In this embodiment, the downstreamend of the drive shaft 435′ constitutes the PTO output shaft 371.

The driven shaft 436′ is bearing-supported by the bearing wall 67′ andan upstream end surface of the HST case 340 so as to be coaxiallyaligned with the input shaft (pump shaft) 301. The driven shaft 436′ andthe input shaft 301 are connected together with their opposite endsabutting each other in such a manner as to be relatively non-rotatablearound the axis. That is, drive power is transmitted from the drivingsource 20 to the input shaft 301 via the driven shaft 436′. It is amatter of course that the speed of drive power may be possibly increasedor reduced between the driven shaft 436′ and the input shaft 301according to the specification of the vehicle.

In this embodiment, the fixed gear 382 of the gear train 380 isrelatively non-rotatably connected with the HST input shaft 301 so thatconstant drive power from the driving source 20 can be inputted into theplanetary carrier 353 serving as the first element. Reference numeral438′ in FIG. 14 is a counter shaft as a constitutional element of therearward-travel power transmission path 430R′.

FIG. 16 is a cross section taken along line XVI-XVI in FIG. 15. Asillustrated in FIG. 16, in this embodiment, the shaft coupling 94 forconnection between the front-wheel-driving-power-take-off-shaft 403 andthe front axle unit 90 is located substantially in the center of thewidth of the vehicle so as to locate the pivotal center of the frontaxle unit 90 substantially in the center of the width of the vehicle.Also, in this embodiment, in order to minimize the vertical length andthe horizontal length of the HMT 30, the drive shaft 435′ (PTO outputshaft 371), the HST input shaft 301 and the HST output shaft 302(running-power intermediate shaft 373) are placed vertically side byside, while the drive shaft 435′ (PTO output shaft 371) is locatedsubstantially in the center of the width of the vehicle, allowingimaginary line F extending through the axes of the respective shafts tobe inclined to the vertical. Whereby, it is possible to minimize thesize of the HMT 30, while preventing an interference with the shaftcoupling 94.

Reference numerals 313 a and 313 b in FIG. 16 respectively represent acontrol shaft and a control arm, which together constitute the outputadjustment member 313. The control arm 313 b has a free end operativelyconnected with the hydraulic piston unit 531. According to thisarrangement, the speed-adjusting hydraulic assembly 530 is controlled soas to pivotally move the control arm 313 b, thereby allowing the controlshaft 313 a to be rotated around the axis and hence thesuction/discharge rate of the hydraulic pump unit 310 to be varied.Reference numeral 313 c in FIG. 16 represents a neutral position returnmechanism provided with a neutral position adjustment function.

The hydraulically actuated clutch 437 is designed to be capable oftaking a forward-travel position for transmitting power from the driveshaft 435′ to the driven shaft 436′ via the forward-travel powertransmission path 430F′, a rearward-travel position for transmittingpower from the drive shaft 435′ to the driven shaft 436′ via therearward-travel power transmission path 430R′, and a neutral positionfor shutting off the power transmission path from the drive shaft 435′to the driven shaft 436′, under the control of a hereinafter describedhydraulic circuit.

In the working vehicle 1′ having the above arrangement, likewise thefirst embodiment, it is possible to downsize the HST, while widening thespeed change range covering both the forward and rearward travel (thatis, the difference in absolute value between the maximum forward travelspeed and the maximum rearward travel speed). Also, it is possible toproduce a desirable effect that adjustment of the HMT to the zero outputcan be roughly made.

In addition, in the working vehicle 1′, by locating of theforward/rearward travel direction changing unit 430′ on the upstreamside of the HMT 30, the forward/rearward travel direction changing unit430′ can be further downsized. That is, with this arrangement, theforward/rearward travel direction changing unit 430′ receives drivepower from the driving source 20 before the speed of the drive power isreduced. Accordingly, it is possible to reduce the load torque appliedto the forward/rearward travel direction changing unit 430′, therebyachieving the downsizing of the forward/rearward travel directionchanging unit 430′.

In the working vehicle 1′, as described above, the driving source 20,the forward/rearward travel direction changing unit 430′ and the HMT 30together constitute the driving-side unit that is supported in vibrationfree manner relative to the vehicle frame 10, and the output from thedriving-side unit is inputted into the separately arranged transmission40′ via the shaft couplings 91, 92. That is, in this embodiment, ofvarious running-power transmission parts or members, main parts ormembers are concentrated in the driving-side unit. With thisarrangement, the working vehicle can easily adjust to its newspecification only by replacing the driving-side unit with a new one.

In this embodiment, vibration-free support of the driving-side unit onthe main frame 11 can be achieved by the brackets 20 a secured to thecrank case (see FIG. 13) and bracket 30 a′ secured to the top side ofthe center section 330 (see FIGS. 1, 15 and 16), the rubber-cushionedbrackets 11 d secured to the opposite lateral sides of the main frames11 closer to the front and rear sides thereof, the rubber cushions 111interposed between the brackets 20 a 30 a and the rubber-cushionedbrackets 11 d. Thus, vibrations of the driving-side unit can beeffectively prevented from transmitting to the vehicle frame 10.

Now, the description will be made for the speed-change control circuitof the working vehicle 1′ of this embodiment mainly with reference todifferences relative to the first embodiment.

FIG. 17 is a speed-change control circuit diagram in the working vehicle1′. A speed-change control mechanism of the working vehicle 1′ includesthe forward pedal 510 and the back pedal 520 (not shown), thespeed-adjusting hydraulic assembly 530 for controlling the slant angleof the output adjustment member 313 in the HST 300, the travel-directionchanging hydraulic assembly 540′ for controlling the forward/rearwardtravel direction changing unit 430′, and the control unit 550 (notshown) for comprehensively controlling the respective units. That is,the working vehicle 1′ is provided with the travel-direction changinghydraulic assembly 540′ in place of the travel-direction changinghydraulic assembly 540 in the first embodiment.

The travel-direction changing hydraulic assembly 540′ includes first andsecond solenoid directional control valves 541 a′, 541 b′ arranged intandem in hydraulic fluid supply/discharge passage for the forwardtravel (hereinafter referred to as “forward-travel hydraulic-fluidsupply/discharge passage”) 545F and hydraulic fluid supply/dischargepassage for the rearward travel (hereinafter referred to as“rearward-travel hydraulic-fluid supply/discharge passage”) 545R.

Specifically, the first solenoid directional control valve 541 a′ isdesigned to be capable of taking an F position enabling theforward-travel hydraulic-fluid supply/discharge passage 545F to becommunicated with pressurized-fluid supply passage 75 and therearward-travel hydraulic-fluid supply/discharge passage 545R to becommunicated with drain passage 76, and an R position enabling therearward-travel hydraulic-fluid supply/discharge passage 545R to becommunicated with the pressurized-fluid supply passage 75 and theforward-travel hydraulic fluid supply/discharge passage 545F to becommunicated with drain passage 76. In FIG. 17, it is held in the Fposition.

The second solenoid directional control valve 541 b′ is designed to becapable of taking a release position enabling the forward-travelhydraulic fluid supply/discharge passage 545F, the rearward-travelhydraulic-fluid supply/discharge passage 545R and the pressurized-fluidsupply passage 75 to be communicated with the drain passage 76, and acommunication position enabling the forward-travel hydraulic-fluidsupply/discharge passage 545F and the rearward-travel hydraulic-fluidsupply/discharge passage 545R to be respectively brought into statesenabling supply of pressurized hydraulic fluid therethrough. In FIG. 17,it is held in the release position.

The first and second solenoid directional control valves 541 a′, 541 b′are controlled by the control part 551 based upon signals from thesensor part 552 in a similar manner as in the first embodiment. That is,for example, once the operation of the forward pedal 510 has beendetected by the sensor part 552, the control part 551 shifts the firstsolenoid directional control valve 541 a′ to the F position based uponthe detected signal from the sensor part 552, and the second solenoiddirectional control valve 541 b′ to the communication position.

A control method of the first and second solenoid directional controlvalves 541 a′, 541 b′ is shown in the following Table 1.

In Table 1, F-mode, N-mode and R-mode respectively represent the forwardtravel mode, the neutral mode and the rearward-travel mode determined bythe control unit 550 based upon the operational statuses of the forwardpedal 510 and the back pedal 520. TABLE 1 F-Mode N-Mode R-Mode FirstSolenoid F position F position R position Directional Control Valve541a′ Second Solenoid Communication Release Communication Directionalposition position position Control Valve 541b′

Thus, in this embodiment, when the control unit 550 has determined basedupon the operational statuses of the forward pedal 510 and the backpedal 520 that the vehicle travel status lies in N-mode, it switches theforward/rearward travel direction changing unit 430′ into a powershutdown mode. Accordingly, the power transmission path to the inputshaft 301 is shut down with the result that the HMT 30 is switched intothe zero output mode.

Preferably, in the N-mode, a power neutral function is also be providedso as to selectively switch the forward/rearward travel directionchanging unit 430′ into a power transmission mode. That is, in thecontrol method as shown in TABLE 1, when the forward pedal 510 and theback pedal 520 are in their inoperative modes, the power transmissionpath from the HMT 30 to the driving wheels are cut off from the drivingsource 20. Thus, the driving wheels are brought into a freely rotatablestate.

The above control method is effective when the working vehicle 1′ isforcibly towed or pressed forward or rearward with the engine 20 stillrunning. However, when the working vehicle 1′ is to be changed in itstravel direction on a slope or the like, the following problem iscaused.

That is, every time when the travel direction of the vehicle is changed,the control unit 550 inevitably detects the N-mode. For example, whenthe mode is switched from the rearward-travel mode to the forward-travelmode, the control unit 550 detects each switching operation for R-modeto N-mode to F-mode. Therefore, when the travel direction of the vehicleis changed in its travel direction such as on a slope, the vehicle 1′may be unintentionally moved downwardly when in the N-mode if theswitching operation is made in the control method as shown in TABLE 1.

In consideration of the above, it is possible to develop a so-calledpower neutral function for example, by operating a power neutral switchprovided near the driver's seat. By the power neutral function is meanta function allowing either a power transmission path (the forward-travelpower transmission path 430F′ or the rearward-travel power transmissionpath 430R′ in this embodiment) to be held in the power transmission modeeven when in the N-mode.

TABLE 2 shows a control method when the power neutral function has beendeveloped. TABLE 2 F-Mode N-Mode R-Mode First Solenoid F position Fposition R position Directional Control Valve 541a′ Second SolenoidCommuni- Communi- Communi- Directional cation cation cation ControlValve position position position 541b′

In the control method as shown in TABLE 2, even when in the N-mode, theforward/rearward travel direction changing unit 430′ is held in thepower transmission mode, it is possible to prevent the vehicle frombeing unintentionally moved downward at the time when the traveldirection is switched such as on a slope. TABLE 2 shows the controlmethod allowing the forward-travel power transmission path 430F′ to bebrought into the power transmission state when in the N-mode.

This embodiment has been described by taking for example the arrangementthat the travel-direction changing hydraulic assembly 540′ includes thefirst and second solenoid directional control valves 541 a′, 541 b′,which are arranged in tandem in the hydraulic-fluid supply/dischargepassages 545F, 545R of the forward/rearward travel direction changingunit 430′. However, the present invention is not necessarily limited tothis embodiment. For example, as illustrated in FIG. 18, thetravel-direction changing hydraulic assembly 540′ may be constructed toinclude first solenoid directional control valve 541 a″ arranged in theforward-travel hydraulic-fluid supply/discharge passage 545F and secondsolenoid directional control valve 541 b″ arranged in therearward-travel hydraulic-fluid supply/discharge passage 545R.

The first solenoid directional control valve 541 a″ is designed to becapable of taking a communication position enabling the forward-travelhydraulic-fluid supply/discharge passage 545F to be brought intocommunication with the pressurized-fluid supply passage 75, and arelease position enabling the forward-travel hydraulic-fluidsupply/discharge passage 545F to be brought into communication with thedrain passage 76. In FIG. 18, it is held in the release position.

The second solenoid directional control valve 541 b″ is designed to becapable of taking a communication position enabling the rearward-travelhydraulic-fluid supply/discharge passage 545R to be brought intocommunication with the pressurized-fluid supply passage 75, and arelease position enabling the rearward-travel hydraulic-fluidsupply/discharge passage 545R to be brought into communication with thedrain passage 76. In FIG. 18, it is held in the release position. Thesecond solenoid directional control valve 541 b″ is preferably aproportional solenoid valve so that rapid hydraulic pressure increase inthe rearward-travel hydraulic-fluid supply/discharge passage 545R can beprevented.

TABLE 3 shows a method of controlling the first and second solenoiddirectional control valves 54la″, 541 b″. TABLE 3 Power Neutral FunctionF-Mode N-Mode R-Mode OFF First solenoid Communication Release positionRelease position directional control position valve 541a″ Secondsolenoid Release position Release position Communication directionalcontrol position valve 541b″ ON First solenoid CommunicationCommunication Release position directional control position positionvalve 541a″ Second solenoid Release position Release positionCommunication directional control position valve 541b″

Thus, the same effect can also be produced by the embodiment asillustrated in FIG. 18.

It is a matter of course that, in this embodiment, the forward pedal 510and the back pedal 520 can be replaced with the forward and back pedal510′ and the forward/rearward travel direction changing member 520′ inthe same manner as in the first embodiment.

According to the working vehicle of the one embodiment, in which thevariable output HST and the planetary gear unit are connected with theengine, which is supported on the vehicle frame closer to either side ofthe fore and aft direction of the vehicle in vibration-free manner,thereby constituting the driving-side unit integrally supported on thevehicle frame in vibration free manner; the transmission case of thetransmission is fixedly supported on the vehicle frame closer to theopposite side of the fore and aft direction of the vehicle with adistance to the driving-side unit; and an output element of theplanetary gear unit is operatively connected with the wheel drive trainof the transmission via the shaft coupling extending along the fore andaft direction of the vehicle, it is possible to expand the speed changerange of the drive axle and/or reduce load applied to the speed changemechanism, as well as secure a free space between the front and rearwheels while effectively limiting expansion of the vehicle's length.

When the shaft coupling is of a vibration absorbing type, it is possibleto effectively prevent vibrations from the engine the main-speed changeunit or the like from transmitting to the transmission, the axle or thelike, and hence prevent the driver from feeling discomfort due tovibrations.

According to the working vehicle of another embodiment, in which thevehicle frame is made up by the pair of main frames that extend in thefore and aft direction of the vehicle on the opposite lateral sidesthereof and the cross member disposed to straddle over the top sides ofthe main frames; and the hydraulic lift unit for moving the attachedworking implement relative the vehicle frame is suspended and supportedby the cross member, load generated during the working implement ismoved can be supported by the vehicle frame. As a result, it is possibleto omit the necessity to make the transmission case or any other membersmore strengthened than they are originally required, and thereforeachieve lowered costs of the transmission case and other members.

With the above arrangement, it is also possible to perform replacementor repair of the hydraulic lift unit without an influence on thetransmission case or any other members.

According to the working vehicle of still another embodiment, which hasthe power transmission path extending from the driving source to thedriving wheels for driving the wheels equipped with the variable outputHMT and the forward/rearward travel direction changing unit arranged intandem therein, in which the HMT is designed to be held in thesubstantially output shutdown mode when the HST variable output is atthe maximum output level in either forward or reverse direction andswitched from the substantially output shutdown mode to the maximumoutput mode as the HST variable output is changed from the maximumoutput level in the either forward or reverse direction to the maximumoutput level in the opposite direction, while the forward/rearwardtravel direction changing unit is designed to shut off the powertransmission path during the HMT is held in the substantially outputshutdown mode, thereby enabling the driving wheels to be brought intofreewheel state, it is possible to expand the running speed change rangewhile minimizing the size of the HST, as well as easily producingfreewheel state of the driving wheels.

By locating the forward/rearward travel direction changing unit locatedon the upstream side of the HMT, the volume of the forward/rearwardtravel direction changing unit can be reduced. Also, the arrangement, inwhich the driving source, the forward/rearward travel direction changingunit and the HMT together constitute the driving-side unit that issupported in vibration free manner relative to the vehicle frame,enables the working vehicle to be easily adjusted to a new specificationof the vehicle.

This specification is by no means intended to restrict the presentinvention to the preferred embodiments set forth therein. Variousmodifications to the working vehicle as described herein, may be made bythose skilled in the art without departing from the spirit and scope ofthe present invention as defined in the appended claims.

1.-11. (canceled)
 12. A working vehicle comprising an HMT made up by thecombination of an HST and a planetary gear unit, and a forward/rearwardtravel direction changing unit for changing the rotational direction ofoutput of said HMT, said HMT and said forward/rearward travel directionchanging unit being arranged in tandem in a power transmission pathextending from a driving source to driving wheels, wherein said HSTincludes a hydraulic pump unit and a hydraulic motor unit, at least oneof which being designated as being of a variable displacement type, apump shaft being operatively connected with said driving source fordriving said hydraulic pump unit and a motor shaft being driven by saidhydraulic motor unit, wherein an HST variable output in both forward andreverse directions is outputted via said motor shaft; said HMT isdesigned to be held in a substantially output shutdown mode during saidHST variable output is at a maximum level in either forward or reversedirection, and switched from said substantially output shutdown mode toa maximum output mode as said HST variable output is changed from saidmaximum output level in said either forward or reverse direction to amaximum output level in the opposite direction; and saidforward/rearward travel direction changing unit is interposed betweensaid driving source and said HMT with respect to a power transmissiondirection, and designed to be switched into a forward travel modeenabling transmission of drive power from said driving source to saidpump shaft with the rotational direction of said drive power maintainedin a forward direction, a rearward travel mode enabling drive power fromsaid driving source to said pump shaft with the rotational direction ofsaid drive power changed to a reverse direction, and a neutral modeshutting off a power transmission path from said driving source to saidpump shaft. 13.-14. (canceled)
 15. A working vehicle according to claim12, wherein a PTO drive power having a constant speed of rotation istaken off through a drive shaft of the forward/rearward travel directionchanging unit.
 16. A working vehicle according to claim 12, wherein anormal operation state or a power neutral operation state could beselected, the normal operation state being configured so that saidforward/rearward travel direction changing unit is switched intorespectively said forward travel mode, said rearward travel mode andsaid neutral mode when a traveling operation member is shifted into aforward travel position, a rearward travel position and a neutralposition by a driver, the power neutral operation state being configuredso that said forward/rearward travel direction changing unit is switchedinto respectively said forward travel mode and said rearward travel modewhen said traveling operation member is shifted into said forward travelposition and said rearward travel position by the driver, and switchedinto either said forward travel mode or said rearward travel mode whensaid traveling operation member is shifted to said neutral position. 17.A working vehicle according to claim 16 wherein said selection of saidnormal operation state or said power neutral operation state isperformed by a power neutral operation member operated by a driver.